JP2019016797A - Wiring film for flat panel display, and aluminum alloy sputtering target - Google Patents

Abstract

To provide: a wiring film for a flat panel display, which is arranged to be able to suppress the rise in wiring resistance even if going through a heat hysteresis at a high temperature of 400°C or higher and 500°C or lower, which does not cause a hillock and the like, and which is superior in heat resistance; and a sputtering target to be used for forming the wiring film.SOLUTION: A wiring film for a flat panel display according to the present invention is one to be formed on a substrate. The wiring film comprises a laminate structure in which first and second layers are laminated. The first layer includes at least one high-melting point metal selected from a group consisting of Mo, Ti, Cr, W and Ta; the second layer is made of an Al alloy including a rare earth element and Ni, whose contents are each 0.01 atom% or more; and the total content of the rare earth element and Ni is 0.055 atom% or less.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a wiring film for a flat panel display and an Al alloy sputtering target used for forming the wiring film.

  An Al thin film having a low electric resistivity is used as a wiring film used as an electrode material for flat panel displays such as liquid crystal displays, organic EL displays, and touch panels. However, Al has a low melting point and low heat resistance. Furthermore, Al is easily oxidized in the atmosphere to form a passive film. Therefore, even when the Al thin film is directly connected to the semiconductor layer or the transparent pixel electrode, there is a problem in that the contact resistance is increased by the Al oxide insulating layer formed at the interface, and the display quality of the screen is lowered.

  The following measures have been taken for these problems. First, for heat resistance, a laminated structure is formed by interposing a barrier metal layer made of a refractory metal such as Mo, Ti, Cr, W, and Ta on the surface of Al. By interposing a barrier metal layer having high mechanical strength, hillocks, which are hemispherical projections, are generated, which are generated by stress concentration due to the difference in thermal expansion coefficient between the substrate and Al. In addition, for the purpose of preventing the formation of Al oxide and enabling electrical connection, the barrier metal layer is interposed between the Al thin film and the semiconductor layer or the transparent pixel electrode. Specifically, a laminated wiring thin film in which the barrier metal layer is formed on and / or below the Al thin film is used.

  On the other hand, with the demand for higher definition and lower power consumption of flat panel displays, materials used for thin film transistors (TFTs) used as switching matrices are also being studied. For example, a polysilicon semiconductor such as a low-temperature polysilicon semiconductor or an oxide semiconductor is used from the conventional amorphous silicon for the purpose of higher performance. These semiconductor materials have high carrier mobility, a large optical band gap, and can be deposited at low temperatures, so next-generation displays that require large size, high resolution, and high-speed driving, resin substrates with low heat resistance, etc. Application to is expected.

  A low-temperature polysilicon semiconductor is produced by using a non-single crystalline amorphous silicon or microcrystalline silicon semiconductor thin film, generally through a heating process such as crystallization annealing at about 400 to 500 ° C. and activation annealing after impurity implantation. Is done. Specifically, for example, a semiconductor thin film such as amorphous silicon formed on a substrate by a CVD method or microcrystalline silicon having a relatively small particle size of about 0.1 μm or less is irradiated with laser light. After irradiating the laser beam to locally heat the semiconductor thin film and at least partially melt it, the semiconductor thin film is crystallized into a polycrystal having a relatively large grain size of about 0.3 μm or more in the cooling process. . Such crystallization annealing by laser light irradiation enables thin film semiconductor devices to be processed at a low temperature, so that not only an expensive quartz substrate having excellent heat resistance but also an inexpensive glass substrate can be used. In the activation annealing, the bonding between the impurity implanted into the polysilicon thin film and Si is promoted, the carrier concentration is controlled, and the treatment for recovering the crystal broken by the ion implantation is also performed.

  Thus, in producing low temperature polysilicon, it is exposed to a thermal history of about 400 to 500 ° C. for crystallization annealing and activation annealing, so that the process temperature is relatively higher than that of amorphous silicon.

  Also in oxide semiconductors, laser annealing and high-temperature annealing at about 350 to 500 ° C. are performed to improve the crystalline film quality, and the performance of semiconductor mobility and TFT threshold voltage is improved. Yes.

  Conventional TFTs using amorphous silicon had a maximum thermal history of about 350 ° C during the TFT manufacturing process, so the above-mentioned wiring thin film in which a refractory metal and an Al thin film are laminated should be used without problems. I was able to. However, when a semiconductor material that is exposed to a thermal history of about 400 to 500 ° C., such as low-temperature polysilicon or an oxide semiconductor, is applied to the TFT, the high thermal history causes a high melting point metal such as Al and Mo to be used. Interdiffusion occurs, causing problems such as increased wiring resistance. Alternatively, the stress of the substrate and the wiring thin film is increased by the high thermal history, and the stress diffusion of Al is promoted as it breaks through the refractory metal, thereby causing hillocks on the surface of the wiring thin film. Further, in the side wall portion of the wiring thin film, there arises a problem that side hillocks occur in a portion not covered with the refractory metal. As described above, the heat treatment at 400 ° C. or higher causes different behavior from the heat treatment at less than 400 ° C. Therefore, a wiring film corresponding to the heat treatment at 400 ° C. or higher is required.

  Therefore, when applying low-temperature polysilicon or oxide semiconductor to the semiconductor layer of TFT, instead of using a laminated wiring film of refractory metal and Al thin film as in the case of using amorphous silicon, refractory metal Single-layer wiring thin films have been used. However, refractory metals have a problem of high electrical resistivity.

  As a heat-resistant wiring material excellent in heat resistance up to 400 ° C., that is, prevention of generation of hillocks, the inventors have so far added one or more of Nd, Gd, and Dy to 1.0 atom in total in Patent Document 1. An Al alloy film containing more than 15% and 15 atomic% or less is disclosed.

Japanese Patent No. 2733006

  However, Patent Document 1 relates to a technique that substantially targets amorphous silicon. That is, Patent Document 1 aims to realize heat resistance and low specific resistance in a heating process of about 250 to 400 ° C. after forming an electrode film, which is unavoidable in the TFT manufacturing process. It is not an improvement.

  The present invention has been made paying attention to the above circumstances, and its purpose is to suppress an increase in wiring resistance even if it receives a high temperature thermal history of 400 ° C. or more and 500 ° C. or less, and to generate hillocks or the like. Another object of the present invention is to provide a flat panel display wiring film having excellent heat resistance and a sputtering target used for forming the wiring film.

  A wiring film for a flat panel display that has solved the above problems is a wiring film for a flat panel display formed on a substrate, and the wiring film is a group consisting of Mo, Ti, Cr, W, and Ta. A first layer containing at least one refractory metal selected from: an Al alloy containing 0.01 atomic% or more and less than 0.2 atomic% of at least one of rare earth elements, Ni, and Co; The gist of the invention is that it has a laminated structure in which two layers are laminated.

  It is also a preferred embodiment that a reaction layer containing at least one of the refractory metals and Al is present at the interface between the first layer and the second layer.

  In a preferred embodiment of the present invention, the Al alloy contains 0.01 atom% or more of rare earth elements and 0.01 atom% or more of at least one of Ni and Co.

  In a preferred embodiment of the present invention, the reaction layer is formed by a thermal history of 400 ° C. or higher and 500 ° C. or lower.

  In a preferred embodiment of the present invention, the rare earth element is at least one selected from the group consisting of Nd, La, Gd, Dy, Y, and Ce.

  In a preferred embodiment of the present invention, the reaction layer contains a compound of Al and Mo.

  In a preferred embodiment of the present invention, a wiring film having a laminated structure of the first layer and the second layer is formed in this order from the substrate side, or the laminated layer of the second layer and the first layer. A wiring film having a structure is formed in this order.

  In a preferred embodiment of the present invention, a wiring film having a laminated structure of the first layer, the second layer, and the first layer is formed in this order from the substrate side, and the first layer and the first layer In any case, the reaction layer is formed at the interface with the two layers.

  Moreover, the sputtering target of the present invention that has solved the above problems is a sputtering target used for forming the wiring film for a flat panel display, and the sputtering target is at least one of rare earth elements, Ni, and Co. The above is comprised of 0.01 atomic% or more and less than 0.2 atomic%, with the balance being Al and an Al alloy sputtering target that is an inevitable impurity.

  In a preferred embodiment of the present invention, the sputtering target contains 0.01 atom% or more of rare earth elements and 0.01 atom% or more of at least one of Ni and Co.

  According to the present invention, even when subjected to a thermal history at a high temperature of 400 ° C. or higher and 500 ° C. or lower, an increase in electrical resistivity is suppressed, generation of hillocks is not observed, and a flat having low wiring resistance and high heat resistance. A wiring film for panel display can be provided. Moreover, according to this invention, the sputtering target used for formation of the said wiring film can be provided.

FIG. It is a scanning electron micrograph of the cross section of 1. FIG. It is a scanning electron micrograph of the cross section of 2. FIG. 3 is a scanning electron micrograph of cross section 3. FIG. 4 is a scanning electron micrograph of section 4. FIG. 1 is a transmission electron micrograph of the cross section of FIG. FIG. It is a transmission electron micrograph of the cross section of 2. FIG. 4 is a transmission electron micrograph of section 4. FIG. 8 is a graph showing the relationship between the heat treatment temperature and the electrical resistivity of each wiring film in various laminated wiring films having the three-layer structure of the example. FIG. 5 is a transmission electron micrograph of the cross section of FIG. FIG. 5 is a scanning transmission electron micrograph of section 5. FIG. 6 is a transmission electron micrograph of section 6. FIG. 6 is a scanning transmission electron micrograph of the cross section of FIG. FIG. 5 is a transmission electron micrograph of the plane of the second layer of No. 5; FIG. 5 is a scanning transmission electron micrograph of the plane of the second layer of No. 5; FIG. 6 is a transmission electron micrograph of the plane of the second layer of FIG. FIG. 6 is a scanning transmission electron micrograph of the plane of the second layer of FIG.

  The present inventors provide a wiring film for a flat panel display, which is excellent in heat resistance without generation of hillocks and the like, in which an increase in wiring resistance is suppressed even when a high temperature thermal history of 400 ° C. or more and 500 ° C. or less is received. In order to do so, it has been studied repeatedly. As a result, in a wiring film comprising a laminated structure of a refractory metal layer such as Mo and Al wiring, rare earth elements such as Nd, La, Gd, Dy, Y, and Ce (hereinafter “REM” (rare) are used as the Al wiring material. It has been found that an Al alloy containing at least one alloy element of Ni and Co in an extremely lower amount than in the past may be used. That is, a reaction layer functioning as a barrier layer for preventing the mutual diffusion of Al and a refractory metal is formed at the interface while effectively exerting the heat resistance improving effect by addition of the alloy element, and becomes a diffusion path. The inventors have found that the increase in wiring resistance can be suppressed because the field density is low, and the present invention has been completed.

  The background to the present invention is as follows. First, regarding interdiffusion between refractory metals such as Mo and Al wiring, the finer the structure of the Al wiring and the higher the grain boundary density, the more the above-mentioned interdiffusion is promoted and the rate of increase in wiring resistance is larger. I understood. The one with the coarsest structure and the low grain boundary density is pure Al, but pure Al is inferior in heat resistance. For this reason, when a heat history of 400 ° C. or higher is received in a state where the refractory metal is laminated, side hillocks are generated as shown in examples described later. When the side hillock occurs, the upper gate insulating film and the protective film are pierced, causing a problem such as current leakage and deterioration of characteristics of the TFT element.

  Therefore, the present inventors have focused on alloying elements so that an increase in wiring resistance due to mutual diffusion between the refractory metal and the Al wiring can be suppressed and an Al alloy having excellent heat resistance can be obtained. As a result, an Al alloy in which at least one of rare earth elements, Ni, and Co is added so that the total content is less than 0.2 atomic% is relatively large in structure grain and close to pure Al. It was found that the grain boundary density can be lowered.

  When a high thermal history of 400 ° C. or more is added to this, a high temperature mainly through an Al grain boundary is formed from the first layer containing the refractory metal in contact with the second layer made of the Al alloy to the second layer side. Melting of the melting point metal, that is, grain boundary diffusion occurs. In an Al alloy, grain boundary diffusion for diffusing grain boundaries is larger than intragranular diffusion for diffusing inside crystal grains. For this reason, when using an Al alloy in which the total content of the alloy elements of the Al alloy is significantly reduced as described above as defined in the present invention, the above-mentioned grain boundary diffusion slightly progresses, but competes with the grain boundary diffusion. Formation of a reaction layer containing at least Al and a refractory metal also proceeds at the interface between the first layer and the second layer, and as a result, formation of the reaction layer at the interface is terminated in advance. This reaction layer effectively functions as a barrier layer for preventing interdiffusion between Al and the refractory metal, and the grain boundary diffusion stops. As a result, it is assumed that the increase in wiring resistance is suppressed.

  From the experimental results, it was found that the wiring resistance was as follows. It is known that the electrical conductivity of the wiring film is hindered by impurity scattering of electrons caused by additive elements and grain boundary scattering caused by the grain boundaries. No. used in Experiment 3 When comparing the electrical resistivity of only the second layers of Nos. 5 and 6, No. 5 using an Al alloy containing Ni and La was obtained. 6 is No. 6 using pure Al. Compared with 5, it shows high electrical resistivity. However, no. When the Al alloy 6 was laminated with Mo and heat-treated at 450 ° C., it exhibited an electrical resistivity equivalent to or lower than that of a pure A1 thin film single layer. No. When the crystal grain sizes of Nos. 5 and 6 were examined, no. 5 is about 200 nm as shown in FIG. 6 had a crystal grain size as large as 500 nm or more as shown in FIG. For this reason, No. 1 using an Al alloy was used. The reason why the electrical resistivity of 6 was lowered is considered to be that grain boundary density was reduced by the coarsening of Al crystal grains and grain boundary scattering was suppressed.

  In addition, No. The reason why the crystal grain size of No. 6 has increased is considered to be the effect of addition of Ni. Compared with the case where only other transition metals or only rare earth elements were added, Ni was particularly effective in increasing Al crystal grains. Furthermore, if the addition amount of Ni was appropriately controlled, an increase effect of Al crystal grains could be exhibited while suppressing an increase in electrical resistivity.

  Moreover, the following things were understood about heat resistance. No. No hillocks were generated even at a high temperature heat treatment of 450 ° C. 6, but such excellent heat resistance was not only due to the addition of alloy elements and the laminated structure, but also due to the diffusion of Mo through the Al grain boundary. This is considered to be a synergistic effect. The relationship between the laminated structure and heat resistance is that by providing a first layer containing Mo as an underlayer between the substrate and the second layer, the orientation of the Al crystal grains is improved and excellent heat resistance is obtained. Furthermore, by providing a third layer containing Mo in the second layer opposite to the substrate, generation of hillocks can be suppressed up to approximately 350 ° C. The relationship between the alloy element and the heat resistance can be improved by making the second layer a predetermined A1 alloy as described above. Further, regarding the relationship between the grain boundary diffusion of Mo and the heat resistance, the grain boundary diffusion of Mo is started when the heat treatment temperature is 350 ° C. or higher, and the grain boundary diffusion further proceeds when the heat treatment temperature is 400 ° C. or higher. The reason for having excellent heat resistance even at a high temperature of 350 ° C. or higher is considered as follows. When the alloy element is added, the grain boundary density increases, and accordingly, the diffusion of Mo is promoted. Therefore, by adding an appropriate amount of the alloy element, heat resistance exceeding the heat resistance improvement effect of the alloy element itself can be obtained by diffusion of Mo, and an increase in resistance is also suppressed. When the heat treatment temperature exceeds 400 ° C., generation of hillocks can be suppressed by Mo that has already diffused through the grain boundaries.

  In addition, No. No. 5 is presumed that since the second layer was pure Al, hillocks were generated around 300 ° C., and the heat resistance improvement effect due to Mo grain boundary diffusion was not obtained. On the other hand, no. In No. 6, the composite heat resistance improvement effect is obtained, and even if the heat treatment temperature is increased, the heat resistance is not interrupted as in the case of pure Al. Thus, no. In No. 6, the type of additive element is appropriately selected, and the heat resistance improvement effect by grain boundary diffusion can be obtained by adopting a laminated structure with Mo. High heat resistance can be achieved.

  As described above, from the viewpoint of reducing the wiring resistance, it is preferable to promote the formation of a reaction layer to suppress the grain boundary diffusion of a refractory metal such as Mo. On the other hand, the heat resistance at 350 ° C. or higher, more preferably 400 ° C. or higher, can be improved by the grain boundary diffusion. In the present invention, considering the balance between the wiring resistance and the heat resistance due to the grain boundary diffusion of the refractory metal, the alloy element of the Al alloy constituting the second layer and its addition amount, and the refractory metal of the first layer to be laminated are appropriately selected. Need to control.

  The wiring film of the present invention includes a first layer containing at least one refractory metal selected from the group consisting of Mo, Ti, Cr, W, and Ta; and at least one of rare earth elements, Ni, and Co Is characterized in that it has a laminated structure in which a second layer of an Al alloy containing 0.01 atomic% or more and less than 0.2 atomic% as an alloy element is laminated.

  First, an Al alloy constituting the second layer that most characterizes the wiring film will be described.

[At least one of rare earth elements, Ni, and Co is 0.01 atomic% or more and less than 0.2 atomic%]
Rare earth elements, Ni, and Co are all elements that contribute to improving the heat resistance of Al, and by further laminating with the first layer as will be described later, further improving the heat resistance in a high temperature range of 400 to 500 ° C. Contribute.

  The rare earth element used in the present invention means lanthanoid elements composed of 15 elements from La to Lu, Sc, and Y. Preferred rare earth elements are Nd, La, Gd, Dy, Y, or Ce, and these can be used alone or in combination of two or more. Nd, La, Gd, and Dy are more preferable, and Nd and La are more preferable.

  In order to exhibit the above effects, the Al alloy of the present invention must contain at least one alloy element of at least one of these rare earth elements, Ni, and Co, preferably 0.02 atom. % Or more, more preferably 0.05 atomic% or more.

  On the other hand, from the viewpoint of improving heat resistance, it is desirable that the content of the alloy element is large. However, if the content of the alloy element is excessive, the crystal grain becomes smaller and the grain boundary density increases, so the second layer along the grain boundary. Since the refractory metal diffusing inside increases, the wiring resistance increases remarkably. Therefore, the total content of the alloy elements contained in the Al alloy needs to be less than 0.2 atomic%, preferably 0.15 atomic% or less, more preferably 0.12 atomic% or less.

  From the viewpoint of obtaining an excellent heat resistance improvement effect, the rare earth element content is preferably 0.01 atomic% or more. On the other hand, the upper limit of the rare earth element content is acceptable up to less than 0.2 atomic%, which is the upper limit of the alloy element content from the viewpoint of heat resistance, but the wiring resistance in the high temperature region at 400 ° C to 500 ° C is further increased. From the viewpoint of reduction, it is preferably 0.05 atomic% or less. The rare earth element content is more preferably 0.02 atomic% or more, still more preferably 0.035 atomic% or more, more preferably 0.15 atomic% or less, still more preferably 0.10 atomic% or less. . Here, the rare earth element content is a single amount when a rare earth element is contained alone, and a total amount when two or more rare earth elements are used in combination.

  Further, from the viewpoint of sufficiently exerting the effect of improving the heat resistance and the effect of suppressing the increase in wiring resistance, the content of at least one or more of Ni and Co (hereinafter sometimes simply referred to as “Ni, Co”) is preferably 0.00. It is 01 atomic% or more, more preferably 0.02 atomic% or more. On the other hand, the upper limit of the content of Ni and Co can be allowed up to less than 0.2 atomic% of the upper limit of the alloy element content from the viewpoint of heat resistance. However, if excessively contained, the wiring resistance becomes higher, and therefore preferably 0. .1 atomic% or less, more preferably 0.08 atomic% or less. Ni and Co may be added singly or in combination. Ni or Co is the amount when either one is included, and the total amount when both are included.

  In the present invention, an alloy element may be added alone, or two or more kinds of alloy elements may be used in combination. If the alloy element in the Al alloy is included in the above range, an effect of improving heat resistance can be obtained. In order to obtain a more excellent heat resistance improvement effect, it is recommended to contain a rare earth element and at least one of Ni and Co. In particular, since Ni and Co have a large effect of increasing Al crystal grains, they preferably contain at least one of Ni and Co.

  As described above, the Al alloy used in the present invention contains at least one of rare earth elements, Ni, and Co in a range of 0.01 atomic% or more and less than 0.2 atomic%, with the balance being Al and inevitable impurities. is there. Preferably, it contains a rare earth element and at least one of Ni or Co, and the balance is Al and inevitable impurities.

  Further, the Al alloy of the present invention includes (i) at least one selected from the group consisting of Mo, Ti, Cr, W, and Ta, as long as the effects of the present invention are not impaired; May contain at least one or more.

  (I) At least one selected from the group consisting of Mo, Ti, Cr, W, and Ta has a heat resistance of the Al alloy in a high thermal history of 400 ° C. or more and 500 ° C. or less as long as it is 0.01 atomic% or more. It effectively works to suppress the formation of hillocks and Al oxides. Moreover, if the content of these alloy elements is a small amount of less than 0.05 atomic%, the wiring resistance can be kept low even when alloying. Furthermore, since the formation of the reaction layer can suppress the diffusion of the high melting point metal from the first layer through the Al grain boundary, it is presumed that the increase in wiring resistance due to the mutual diffusion can also be suppressed.

  The content of at least one selected from the group consisting of Mo, Ti, Cr, W, and Ta is preferably 0.01 atomic% or more, more preferably 0.02 atomic% or more, and preferably 0 .05 atomic% or less, more preferably 0.03 atomic% or less. These alloy elements may be added alone or in combination. When any one is included, it is the amount, and when any is included, it is the total amount.

  (Ii) Cu and Ge are elements that precipitate at a lower temperature than the above-mentioned rare earth elements, Ni and Co, and do not adversely affect the grain boundary density, so that an increase in wiring resistance can be suppressed. In order to obtain such an effect, the content of at least one of Cu and Ge is preferably 0.01 atomic% or more, more preferably 0.02 atomic% or more. On the other hand, if the content of Cu or Ge is excessively increased, the wiring resistance is increased, so that it is preferably 0.05 atomic% or less, more preferably 0.03 atomic% or less. Cu and Ge may be added alone or in combination. When either one is included, it is the amount, and when both are included, it is the total amount.

  Note that (i) at least one or more selected from the group consisting of Mo, Ti, Cr, W, and Ta; (ii) at least one or more of Cu and Ge; That is, the total amount of rare earth elements, Ni, Co and the above (i) and (ii) needs to be controlled to be less than 0.2 atomic%. When the total amount is 0.2 atomic% or more, problems such as an increase in wiring resistance after heating may occur. The preferable range of the total amount is as described above.

  The Al alloy that constitutes the second layer has been described above. Hereinafter, the wiring film of the present invention will be described.

  In the wiring film of the present invention, a first layer containing at least one refractory metal selected from the group consisting of Mo, Ti, Cr, W, and Ta and a second layer made of the Al alloy are laminated. It is a laminated structure. Specifically, a two-layer structure in which the first layer and the second layer are laminated in this order in order from the substrate side may be employed, and the second layer and the first layer may be arranged in this order. A laminated two-layer structure may be used. Alternatively, a three-layer structure in which the first layer is disposed above and below the second layer may be used. That is, a three-layer structure in which the first layer, the second layer, and the first layer are stacked in this order from the substrate side may be used. In the present invention, when a three-layer structure is used, the first layer laminated on the side opposite to the substrate side when viewed from the second layer may be referred to as a third layer.

  In particular, a three-layer structure is desirable because the oxidation resistance of the Al alloy as the second layer is improved and the heat resistance is further improved.

  The refractory metal used in the first layer of the present invention is usually used as a barrier layer in the technical field of flat displays. The refractory metal diffuses along the Al grain boundary and contributes to an improvement in heat resistance. Specifically, it can be used as an alloy element containing one or more of Mo, Ti, Cr, W, and Ta. When the first layer is disposed above and below the second layer, the upper first layer and the lower first layer may have the same composition or may be different. The first layer may contain an element other than the refractory metal, but is preferably any refractory metal and the balance: inevitable impurities.

  The wiring film of the present invention has any laminated structure, but at the interface between the first layer and the second layer, and moreover at the interface between the second layer and the third layer in the case of a three-layer structure. A reaction layer containing at least Al and a refractory metal is formed. The reaction layer in the present invention is formed by a high temperature thermal history to which low temperature polysilicon or an oxide semiconductor is exposed, preferably 400 ° C. or more and 500 ° C. or less. By setting the upper limit of the thermal history to 500 ° C. or less, the reaction layer does not grow any more and stays at the interface, so that an increase in electrical resistance can be effectively suppressed. Examples of the reaction layer include a compound containing Al and a refractory metal, specifically, a compound containing a compound of Al and Mo.

  The reaction layer can be confirmed by observing a cross section of the wiring film having a laminated structure after heat treatment with a transmission electron microscope (hereinafter sometimes referred to as “TEM” (Transmission Electron Microscope)) as shown in Examples.

  The substrate used in the present invention is not particularly limited as long as it is usually used in the field of flat panel displays, and examples thereof include those made of metal such as glass, quartz, silicon, SUS, and Ti foil.

  The flat panel display of the present invention includes the above-described wiring film of the present invention, and examples thereof include a liquid crystal display, an organic EL display, a touch panel, a field emission display, a vacuum fluorescent tube display, and a plasma display.

  In the flat panel display, the semiconductor layer of the thin film transistor is preferably made of low-temperature polysilicon or oxide. As described above, these may be subjected to a high-temperature thermal history of 400 ° C. or more and 500 ° C. or less for the purpose of their production process or film quality improvement. However, if the wiring film of the present invention is used, the heat resistance and wiring resistance are increased. The advantages of these semiconductor layer materials can be enjoyed to the maximum without adversely affecting the process. The oxide is not particularly limited, and examples thereof include oxides containing at least one element selected from the group consisting of commonly used In, Zn, Ga, and Sn.

  The Al alloy thin film characterizing the present invention is preferably formed by a sputtering method using a sputtering target (hereinafter also referred to as “target”). Examples of the thin film forming method include an ink jet coating method, a vacuum deposition method, and a sputtering method. Among these methods, the sputtering method is preferable because it is easy to alloy and has excellent film thickness uniformity.

  When the Al alloy film is formed by the sputtering method, an Al alloy sputtering target having the same composition as the desired Al alloy film and containing a predetermined amount of at least one of rare earth elements, Ni, and Co is used as the sputtering target. Thus, there is no risk of composition deviation, and an Al alloy film having a desired component composition can be formed. You may co-evaporate using a several sputtering target so that it may become Al alloy film of a desired component composition.

  The sputtering target used for forming the first wiring film contains 0.01 atomic% or more and less than 0.2 atomic% of at least one of rare earth elements, Ni, and Co, and the balance is Al and inevitable impurities. It is an Al alloy sputtering target. Preferably, the rare earth element is 0.01 atomic% or more, and at least one of Ni and Co is 0.01 atomic% or more, and the total alloy element content is less than 0.2 atomic%. , Balance: Al and an Al alloy sputtering target which is an inevitable impurity.

  In the sputtering target, (i) at least one or more selected from the group consisting of Mo, Ti, Cr, W, and Ta; (ii) at least one or more of Cu and Ge; It may be included in the amounts described above.

  Examples of the method for producing the sputtering target include a vacuum melting method and a powder sintering method. In particular, the production by the vacuum melting method is desirable from the viewpoint of ensuring the composition in the target surface and the uniformity of the structure.

  The wiring resistance of the wiring film of the present invention varies depending on the structure of the flat panel display, wiring rules, etc., but is generally 5.5 μΩcm or less, preferably 5.0 μΩcm or less.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Experiment 1 (Evaluation of heat resistance)
On the glass substrate, in order from the substrate side, a first layer made of Mo with a thickness of 70 nm, a second layer made of an Al—Ni—La alloy with a thickness of 300 nm having the composition shown in Table 1, and a film thickness made of Mo with a thickness of 70 nm. The first layer (hereinafter referred to as “third layer”) was sequentially laminated using a sputtering method. In addition, No. 2-No. The second layer 4 was deposited using a sputtering target having a composition corresponding to the film. At this time, the ratio of the DC power was controlled so that the second layer had the composition shown in Table 1. No. As the second layer 1, a pure Al film having a thickness of 300 nm was formed using a pure Al sputtering target. The composition of the second layer was confirmed by quantitative analysis using an ICP emission spectroscopic analyzer. In the table, at% means atomic%.

The sputtering conditions are as follows.
DC magnetron sputtering system Target size: 4 inches φ × 5mmt
Ar gas pressure: 2 mTorr
DC power: 250W
Distance between electrodes: 100mm
Substrate temperature: room temperature

  Next, a line and space pattern having a width of 5 μm was formed by photolithography and etching, and then heat treatment was performed at 400 ° C. and 450 ° C. for 1 hour in a nitrogen atmosphere by infrared heating.

  The heat resistance of each obtained sample was evaluated. Specifically, the cross section of the sample was observed with a scanning electron microscope (SEM) from the diagonally upward direction of the laminated wiring after the heat treatment, and the presence or absence of side hillocks was examined. The magnification was in the range of 3000 to 10,000 times. The case where side hillock generation was observed was rated as x, and the case where side hillock generation was not observed was marked as ◯. The results are shown in Table 1.

  From Table 1, No. In Nos. 2 to 4, no side hillock was observed at any heating temperature. Also, no side hillock was seen at the end of the wiring. On the other hand, no. No. 1 was confirmed to be formed with high density of protrusions called side hillocks at the end of the wiring at any heating temperature.

  1-4 show No. 1 after heating to 450 ° C. 1 to 4 are SEM photographs, but as shown in FIG. It was confirmed that the protrusion 1 corresponding to the side hillock 1 was generated from the end of the wiring. On the other hand, as shown in FIGS. In 2-4, the protrusion did not arise.

  Furthermore, the result of having observed the cross section of the laminated wiring after heating at 450 degreeC with the TEM dark field image is shown to FIGS. As shown in FIGS. 5 to 7, the Mo—Al reaction layer 2 was confirmed between the first layer 3 and the second layer 4, and between the second layer 4 and the third layer 5. 5 to 7 are respectively No. 1, 2, 4 but no. It was found that the region of the reaction layer expanded as the amount of addition of 1, 2, 4 and alloy elements increased.

Experiment 2 (Evaluation of wiring resistance)
Each sample was prepared in the same manner as in Experiment 1 except that a line and space pattern having a width of 100 μm and a length of 10 was formed. In this example, a sputtering apparatus was used in which the distance between the electrodes was set to 100 mm instead of the usual 55 mm. Therefore, in this embodiment, gas components such as oxygen, nitrogen, and moisture remaining mainly in the sputtering chamber taken into the film are increased compared with the case where the film is formed at a distance of 55 mm, and the electric resistivity is 20%. It showed a tendency to become higher.

  The electrical resistance of the second layer in the obtained multilayer wiring was measured by a four-terminal method to evaluate the wiring resistance. The wiring resistance is considered to be the parallel resistance of Mo and Al. The resistivity of Mo is 12 μΩcm parallel resistance before and after the heat treatment, and the electric resistivity of the Al alloy is calculated by distributing and subtracting the resistance by the film thickness ratio of the laminated wiring. did. For reference, the electrical resistivity of the second layer at 24 ° C. before the heat treatment was measured in the same manner (“asdepo” column in the table). In this example, an electrical resistivity of 5.5 μΩcm or less was excellent in wiring resistance, and the wiring resistance exceeding 5.5 μΩcm was evaluated as being high and rejected.

These results are shown in FIG. From FIG. When 1 to 3 were used, the electrical resistivity could be kept low at 5.5 μΩcm or less regardless of whether the heating temperature was 400 ° C. or 450 ° C.
Specifically, No. 1 using pure Al for the second layer. The electrical resistivity of 1 (♦ in the figure) tended to increase as the heating temperature increased, but the degree was very low.
Further, No. 2 made of an Al alloy satisfying the requirements of the present invention in the second layer. The electrical resistivity of 2, 3 (■, ▲ in the figure) also showed a tendency to increase as the heating temperature increased, but it could be suppressed within the acceptable standard electrical resistivity range. The rate of increase was higher than that of pure Al.
In contrast, no. 4 (● in the figure) is an example in which the total content of alloy elements contained in the Al alloy film as the second layer is as high as 0.22 atomic%, and the electrical resistivity increased.

  From the results of the above experiments 1 and 2, No. 1 containing an Al alloy as defined in the present invention. When two or three wiring films are used, even if a high temperature thermal history of 400 ° C. or more and 500 ° C. or less is received, an increase in wiring resistance is suppressed, and there is no generation of side hillocks and excellent flat panel display with excellent heat resistance It was confirmed that

  On the other hand, no. In No. 1, the electric resistivity after the heat treatment tended to gradually increase when the heating temperature exceeded 400 ° C., but the degree was very low. However, when pure Al is used, the heat resistance is lowered, and when pure Al is used, side hillocks are generated after the heat treatment.

  No. 4 is an example in which an Al alloy having an excessive alloy element content is used for the second layer. No. No side hillock was observed in heat treatment 4 and heat resistance was good, but as shown in FIG. 8, the electrical resistivity after the heat treatment markedly increased when the heating temperature exceeded 400 ° C. The rate of increase was much higher than that of pure Al.

Experiment 3
No. 5 and 6 are formed by sequentially using a sputtering method on a glass substrate in order from the substrate side, a first layer made of Mo having a thickness of 70 nm, a second layer having a thickness of 1000 nm, and a third layer made of Mo having a thickness of 70 nm. And laminated. In addition, No. The second layer of No. 5 is a pure Al film. The second layer 6 is an Al-0.02 at% Ni-0.04 at% La alloy film. Vapor deposition was performed using a sputtering target having a composition corresponding to each film. The sputtering conditions are the same as in Experiment 1. The composition of the second layer was confirmed in the same manner as in Experiment 1.

  Next, heat treatment was performed for 1 hour at a temperature of 450 ° C. in a nitrogen atmosphere by infrared heating to prepare a sample.

  Each obtained sample was observed from various angles. First, the result of having observed the cross section of each sample after heat processing by the TEM dark field image is shown in FIG. Moreover, the result of having observed the same cross section as this TEM observation cross section by STEM (Scanning Transmission Electron Microscope: Scanning Transmission Electron Microscope) is shown in FIGS.

No. 5 is shown in FIGS. As shown in FIG. 10, there is a bright portion in the grain boundary portion in the direction from the first layer to the second layer. : EDS), it was confirmed that Mo was diffused along the grain boundary. Further, a bright portion exists at the interface between the first layer and the second layer. As a result of examining this portion by electron diffraction, Al ₁₂ Mo formed by reaction of Al and Mo is obtained. Was confirmed.

No. 6 is shown in FIGS. As shown in FIG. 11, in the grain boundary part of the second layer, there is a bright part in the direction from the first layer to the second layer, and Mo is diffused along the grain boundary. Was confirmed. The are also present bright contrast portions at the interface of the first and second layers, Al and Mo Al are formed by reacting 12 _Mo, the reaction layer was confirmed.

  In addition, based on FIGS. 5 and no. As a result of comparing the size of Al crystal grains of No. 6, 6 was bigger.

  Next, no. 5, no. 13 and 15 show the results of observing a flat surface exposed by cutting the second layer portion in the horizontal direction with a TEM dark field image, respectively. Based on FIGS. 5 and no. As a result of comparing the size of Al crystal grains of No. 6, 6 was bigger.

  In addition, the above No. 5 and no. FIGS. 14 and 16 show the results of STEM observation of the TEM observation of the exposed plane obtained by cutting the second layer portion 6 in the horizontal direction. As shown in FIG. 14, a bright part along the grain boundary part, that is, a Mo diffusion layer in which Mo diffused along the grain boundary was confirmed. Similarly, the Mo diffusion layer was confirmed in FIG. Further, when comparing the area ratios of the Mo diffusion layers based on FIGS. 6 was bigger.

1 protrusion corresponding to side hillock 2 reaction layer 3 first layer 4 second layer 5 third layer 6 Mo reaction layer 7 Mo diffusion layer

Claims (8)

A wiring film for a flat panel display formed on a substrate,
The wiring film includes a first layer containing at least one refractory metal selected from the group consisting of Mo, Ti, Cr, W, and Ta;
It has a laminated structure in which a second layer made of an Al alloy containing rare earth elements and Ni in an amount of 0.01 atomic% or more and a total content of the rare earth elements and Ni of 0.055 atomic% or less is laminated. A wiring film for a flat panel display.   The wiring film for a flat panel display according to claim 1, wherein a reaction layer containing at least one kind of the refractory metal and Al is provided at an interface between the first layer and the second layer.   The wiring layer for a flat panel display according to claim 2, wherein the reaction layer is formed by a thermal history of 400 ° C. or more and 500 ° C. or less.   The wiring film for a flat panel display according to claim 1, wherein the rare earth element is at least one selected from the group consisting of Nd, La, Gd, Dy, Y, and Ce.   The wiring film for a flat panel display according to claim 2, wherein the reaction layer contains a compound of Al and Mo.   In order from the substrate side, the wiring film of the laminated structure of the first layer and the second layer is formed in this order, or the wiring film of the laminated structure of the second layer and the first layer is arranged in this order. The wiring film for flat panel displays of any one of Claims 1-5 formed.   In order from the substrate side, a wiring film having a laminated structure of the first layer, the second layer, and the first layer is formed in this order, and at the interface between the first layer and the second layer, In any case, the wiring film for a flat panel display according to any one of claims 2, 3 and 5, wherein the reaction layer is formed. A sputtering target used for forming a wiring film for a flat panel display according to claim 1,
The sputtering target contains 0.01 atomic% or more of a rare earth element and Ni, respectively, the total content of the rare earth element and Ni is 0.055 atomic% or less, and the balance: Al and an inevitable impurity Al alloy Sputtering target.